A substrate holding apparatus is known as a device for holding a periphery of a substrate, such as a wafer, and rotating the substrate. Such a substrate holding apparatus is used in a processing apparatus, such as a drying apparatus for drying a substrate by spraying an IPA vapor onto a surface of a substrate while rotating the substrate.
The above-described substrate holding apparatus includes a plurality of support posts for supporting a periphery of a substrate. These support posts are arranged along the periphery of the substrate. A spring is disposed around each of the support posts so that the support posts are biased downwardly by the springs. The support posts are elevated by a lifter. When the substrate is transferred from a transfer robot to the substrate holding apparatus, the support posts are elevated by the lifter against the forces of the springs. When the substrate is to be processed while the substrate holding apparatus is to rotate the substrate, the lifter moves down and the support posts are forced downwardly by the springs.
During processing of the substrate, the substrate is rotated around its axis. There has recently been a demand to rotate a substrate as fast as possible in order to increase a throughput of the processing of the substrate. However, when the substrate is rotating at a high speed, strong centrifugal forces act on the springs disposed around the support ports, thus causing the springs to deform outwardly. Such deformation of the springs generates large stresses in the springs, which can fatigue the springs. As a result, the springs may be broken before expiration of an expected lifetime of the springs.
Further, when the substrate is rotating at a high speed, strong centrifugal forces act also on the support posts, thereby causing outward displacement of respective ends of the support posts. As a result, the substrate, supported by the support posts, can become unstable.